Hemophilia is sometimes called “the royal disease” because of its presence among members of European royal families in the 1800s and 1900s. For example, historians think that Queen Victoria of England (who ruled from 1837 to 1901) was a carrier of hemophilia B and passed it on to at least three of her nine children.
Of course, royalty isn’t actually considered a risk factor for hemophilia B. Race, sex, and age play the most prominent roles in who gets hemophilia B.
Hemophilia B is a bleeding disorder in which a person’s blood doesn’t properly clot to control bleeding. Although many people develop hemophilia B from sporadic (random) genetic changes, this condition — like other types of hemophilia — is most often inherited from parents. Because of the way hemophilia B is passed down to children, it is much more common in males. The biggest risk factors for developing hemophilia B are having a family history of hemophilia B and being male.
Hemophilia B goes by many names. It was originally called Christmas disease — named for one of the first people discovered to have this disease in the 1950s. Some countries, such as the United Kingdom and Australia, use the spelling “haemophilia B” for the same condition. Hemophilia B is also called factor IX (9) deficiency, which refers to its cause — a lack of the clotting factor known as factor IX. (You will usually see Roman numerals in any discussion of clotting factors.)
People whose blood contains less factor IX may bleed longer and more often than others.
Hemophilia B symptoms are classified by severity, based on the percentage of factor IX available to form a clot in a person’s blood. Normal plasma levels are between 50 percent and 150 percent, according to the National Hemophilia Association.
Symptoms of mild hemophilia B — defined as 6 percent to 49 percent of factor IX — include:
Symptoms of moderate hemophilia B — 1 percent to 5 percent of factor IX — include:
Symptoms of severe hemophilia B — less than 1 percent of factor IX — include:
In addition, babies with severe hemophilia B may be irritable and unable to walk or crawl.
It’s hard to know how many people have hemophilia B because some people with mild hemophilia B may not know they have the disorder.
A study released in 2020 looked at data from hemophilia treatment centers (HTCs) in the United States. Data collection took place from 2012 to 2018 to estimate the number of U.S. males living with hemophilia. The researchers found that about 3.7 per 100,000 males have hemophilia B. They also determined that about 1 in every 19,283 males born from 1995 to 2014 had hemophilia B.
However, the actual rates are likely higher, because the study did not include females or the estimated 20 percent of people who were treated outside of HTCs.
Hemophilia B occurs in all types of people, but researchers are still trying to determine whether it’s more prevalent among people of particular races or ethnicities.
The 2020 study compared the prevalence (number of affected people) of hemophilia among Hispanic, Black, and non-Hispanic white males in the U.S. The study didn’t specify whether hemophilia B was more or less prevalent in certain groups compared to hemophilia A.
The overall prevalence of hemophilia was:
The study suggests race and ethnicity may play a role in the prevalence of hemophilia. However, citing this study, The Coalition for Hemophilia posted, “As far as we know, the incidence of hemophilia is the same regardless of race or ethnicity. That is, everyone has the same chance of being born with hemophilia. The difference comes from the risk of death for the group. Blacks and Hispanics tend to live shorter lives than whites in the United States.”
Researchers have also examined whether hemophilia may affect people of some racial and ethnic groups differently than others. One small study found that, among males ages 13 to 25 with hemophilia, the non-white participants were more likely to develop inhibitors. Inhibitors are antibodies produced by the immune system to attack infused clotting factor concentrates. Having inhibitors can make standard replacement treatment less effective or ineffective.
More research is needed to fully understand whether hemophilia B affects members of some racial and ethnic groups more than others — and if so, why.
Hemophilia B is more common in males because it involves sex-linked recessive inheritance. The harmful change (mutation) in the factor IX gene — called the F9 mutation — is located on the X chromosome, which males inherit only from their mother and females inherit from both parents.
The X chromosome determines a person’s biological sex. Biological males have one Y chromosome and one X chromosome. If the mother passes on the F9 mutation on the X chromosome to a male child, they will have hemophilia B.
Biological females have two X chromosomes, so they must inherit the F9 mutation from both parents to develop hemophilia B. Because biological males need only one copy of the mutated X chromosome, they are more likely to develop hemophilia B.
Biological females who inherit just one copy of an X chromosome with the F9 mutation become hemophilia B carriers — they do not have hemophilia B, but they can pass it on to their children. “For each man with hemophilia, 1.6 female carriers can be identified,” according to findings in the Journal of Thrombosis and Haemostasis.
About 24 percent of people with mild hemophilia are females, but it is not common for females to have moderate or severe hemophilia, according to a 2021 study in the journal Haemophilia.
Hemophilia B is usually diagnosed in childhood. More severe hemophilia B is more likely to be diagnosed at an earlier age since the symptoms show up sooner than those of mild hemophilia B:
The average age of males living with hemophilia in the United States is about 23.5 years, and three-quarters are under 35, according to results published in Haemophilia. The 2021 study discussed above reported that the average age of females living with hemophilia is 31.4 years. Because advances in the treatment of hemophilia B have improved life expectancy, you may think that the average age should be closer to that of the general population in the United States — 38.8 years.
However, the 1980s introduction of the human immunodeficiency virus (HIV) and hepatitis C into the blood supply caused the death of many people with hemophilia. The young average age of men with hemophilia B could be due to this population recovering from increased death rates due to HIV and hepatitis C. It’s possible that the average age of females with hemophilia is older because they’re less likely than males to have HIV or hepatitis C, according to the authors of the 2021 study.
Over time, the average age of a person with hemophilia B will probably approach that of the general average.
Hemophilia B is usually inherited from parents, so you can’t lower your risk of developing it. If you have hemophilia B or are a carrier, you also can’t reduce the risk of passing it on to your children.
Genetic tests can look for the mutations that cause hemophilia B. Genetic counseling may be available to help you better understand your and your family’s risk of developing hemophilia B.
Hemophilia B is a lifelong condition that cannot be cured, but it can be treated. Hemophilia treatments and gene therapy have greatly improved the life expectancy and quality of life for individuals with hemophilia. Talk with your health care provider and keep up with your regular hematology appointments to ensure you are getting the best treatment plan.
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